[vsnet-grb-info 19882] GRB 171003A: LT early optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21961
SUBJECT: GRB 171003A: LT early optical observations
DATE:    17/10/03 10:34:35 GMT
FROM:    Cristiano Guidorzi at Ferrara U,Italy  <guidorzi at fe.infn.it>

C. Guidorzi (U. Ferrara), S. Kobayashi (LJMU), C.G. Mundell (U. Bath), 
A. Gomboc (U. Nova Gorica), I.A. Steele (LJMU), T. Laskar (UC Berkeley) 
on behalf of a large collaboration report:

The Liverpool Telescope automatically began observing Swift possible GRB 
171003A (Cenko et al. GCN 21960) on October 03, 02:51:26 UT (14 minutes 
after the GRB trigger time) with RINGO3 polarimeter and IO:O camera in 
the SDSS R filter. In addition to the presence of a couple of catalogued 
bright objects, within the Swift-XRT error circle we very marginally 
detect a possible faint, uncatalogued object at the following position:

RA(J2000) =  02:43:40.65
DEC(J2000)= +61:25:53.6

at ~9" from the bright stars above mentioned, with an error radius of 
about 1" and a magnitude of r'=21.3 +- 0.3 (in a 6x10s frame at 48 
minutes post GRB), as calibrated against Pan-STARRS field stars. The 
same possible source is not detected by us earlier, at a mid time of 19 
minutes post GRB down to r'>20.5 mag. Combining the two measures, a 
corresponding upper limit of alpha<0.8 is obtained on the average 
power-law decay index.